The present invention relates to drive mechanisms, and, more particularly, to such mechanisms in which the rotation of a nut causes a worm to be driven longitudinally.
It is conventional to use worm drive mechanisms to convert rotary motion to longitudinal motion, examples of previously known mechanisms of this type being described in U.S. Pat. Nos. 1,463,899 to McKechnie; 2,286,249 to Abbe and 2,315,571 to Wilder. Generally a worm, formed by a solid, rigid, externally threaded shaft, is driven by the rotation of a nut. When a large longitudinal displacement is required, a worm of suitable length is expensive to manufacture and ship. If the mechanism is attached to a structure that precludes precise alignment, jamming of the mechanism or damage to the threads may result. Moreover, a conventional worm drive mechanism can create an inconvenient or even dangerous situation since the worm may be immobilized or is movable only with great difficulty in the event of a power failure or a malfunction that prevents the nut from turning.
One potential application of worm drive mechanisms in which the above-mentioned disadvantages pose particularly difficult problems is in door opening devices powered by relatively small electric motors. If, for example, the sliding door of an industrial building or aircraft hangar were to be opened by a worm drive mechanism, a very lengthy worm would be required that might render the device impractical, especially when cost limitations are considered, since a worm forty feet or more in length might be needed. The play typically found in doors prevents precise alignment, and the drive mechanism could easily become jammed to prevent the door from being opened quickly in the case of an emergency. In the event of a power failure, it might be necessary to disassemble the mechanism before the door could be opened.
An objective of the present invention is to provide a worm drive mechanism that overcomes many disadvantages mentioned above.